As a skinny kid with a funny name who grew up with white parents and grandparents in Hawaii and for a while in Indonesia, Barack Obama is no stranger to racial insults.

So Rush Limbaugh's description of him as a "Halfrican American" along with the repeated playing of a racially insulting song deriding Obama as a "magic negro" will come as no great surprise. Limbaugh prides himself on being a shock jock but in truth his bigotry is not that shocking.

Nor is the fact that CBS had to disable people from commenting on Obama stories on its website because of the sheer volume and intensity of racist comments.

These things are depressing. They also stand in stark contrast to the ridiculous claim that being black will go in his favour when the polls open. And while they are not inevitable, they are expected. Every time I write on this site I expect it. And I am rarely disappointed.

There is, it seems, a critical mass of white people out there who does not simply loathe what a black person might say, but who hates the idea that they have a voice at all.

The problem is not confined solely to race. And as ever it is the work of a tiny minority. But a very vocal and belligerent one. And somehow their numbers are amplified on the internet, where people hide behind anonymity in a medium for the time being dominated by white men. The result is a curious and irritating form of white noise - a ribald gabfest in which either black people in general or a specific black person in particular become the target for considerable animus.

Despite stellar individual contributions the standard of these conversations only occasionally rises above those you might overhear in a pub. The difference is you chose who you talk to in a pub.

Obama has done well to simply parry these comments and get on with his campaign. But he can only do this for so long. For these remarks do not come in isolation. Some push the boat out and make threats, creating a sense of siege that has a real effect. It was Alma Powell who convinced her husband Colin not to run for president back in the 1990s, for fear of assassination. Now comes news that Obama has secret service protection. I wonder why that would be?